Containers used in determining the thermal stability of fuels

ABSTRACT

A thermal oxidation tester is shown for determining thermal stability of a fluid, particularly hydrocarbons, when subjected to elevated temperatures. The tendency of the heated fluid to oxidize and (1) form deposits on a surface of a heater tube and (2) form solids therein which are both measured at a given flow rate, temperature and time. The measured results are used to determine whether a fluid sample passes or fails the test. Specifically constructed containers used in a thermal oxidation tester are shown. These containers (1) reduce physical contact to hydrocarbon test fuels, (2) reduce exposure to hydrocarbon fuel vapors, (3) reduce environmental impact by reducing chemical spills, and (4) improve overall work flow of test.

CROSS REFERENCE TO RELATED APPLICATIONS

This is a continuation-in-part of U.S. patent application Ser. No.12/838,104, filed on Jul. 16, 2010, having at least one overlappinginventor and the same assignee.

BACKGROUND OF THE INVENTION

1. Technical Field

This invention relates to methods and devices for measuring the thermalcharacteristics of fuels. Specifically, this invention relates tocontainers used in measuring the thermal oxidation tendencies of fuelsfor liquid hydrocarbon-burning engines.

2. Background Art

When engines were developed for use in jet aircraft, problems began todevelop for jet fuel due to poor fuel thermal stability. At highertemperatures, the jet fuels would oxidize and form deposits that wouldclog fuel nozzles and fuel filters. These deposits would also collect inthe jet engine.

While various tests were devised and used in the 1950s and 60s to ratethe thermal oxidation characteristics of jet fuels prior to being usedin jet aircraft, Alf Hundere developed the apparatus and method whichbecame the standard in the industry. In 1970, Alf Hundere filed whatbecame U.S. Pat. No. 3,670,561, titled “Apparatus for Determining theThermal Stability of Fluids”. This patent was adopted in 1973 as ASTMD3241 Standard, entitled “Standard Test Method for Thermal OxidationStability of Aviation Turbine Fuels”, also known as the “JFTOT®Procedure”. This early Hundere patent was designed to test thedeposition characteristics of jet fuels by determining (1) deposits onthe surface of a heater tube at an elevated temperature and (2)differential pressure across a filter due to collection of particulatematter. To this day, according to ASTM D3241, the two criticalmeasurements are still (1) the deposits collected on a heater tube and(2) differential pressure across the filter due to the collection ofparticulate matter on the filter.

According to ASTM D3241, 450 mL of fuel flows across an aluminum heatertube at a specified rate, during a 2.5 hour test period at an elevatedtemperature. Currently six different models of JFTOT®¹ instruments areapproved for use in the ASTM D3241-09 Standard. The “09” refers to thecurrent revision of the ASTM D3241 Standard. ¹ JFTOT is the registeredtrademark of Petroleum Analyzer Company, LP.

While over the years various improvements have been made in theapparatus to run the tests, the basic test remains the same.Improvements in the apparatus can be seen in U.S. Pat. Nos. 5,337,599and 5,101,658. The current model being sold is the JFTOT 230 Mark III,which is described in further detail in the “Jet Fuel Thermal OxidationTester—User's Manual”. The determination of the deposits that occur onthe heater tube can be made visually by comparing to known colorstandards or can be made using a “Video Tube Deposit Rater” sold underthe Alcor mark.

The determination of the amount of deposits formed on the heater tube atan elevated temperature is an important part of the test. The currentASTM D3241 test method requires a visual comparison between the heatertube deposits and known color standard. However, this involves asubjective evaluation with the human eye. To take away the subjectivityof a person, an electronic video tube deposit rater was developed.

Also, there has been considerable discussion as to the polish or finishof the heater tube. (See U.S. Pat. No. 7,093,481 and U.S. PatentApplication Publication No. US 2002/083,760.) The finish of the heatertube is very important in determining the amount of fuel deposits thatwill form thereon. Therefore, it is important that the quality of thefinish on heater tubes made today be consistent with the finish ofheater tubes made since 1973.

In the past, containers used for (1) the test sample or (2) waste fuelhad limitations. The containers were primarily open vessels that did notprovide the operator feedback about being securely positioned, did notcontain or capture fuel vapors, and were difficult to secure in place.Aeration of the test sample while in the container also requires acoarse glass dispersion tube.

BRIEF SUMMARY OF THE INVENTION

It is an object of the present invention to provide an apparatus andmethod for testing thermal oxidation stability of fluids, particularlyaviation fuels.

It is another object of the present invention to provide special purposecontainers for an apparatus and method to measure the tendency of fuelsto form deposits when in contact with heated surfaces.

It is another objective of the present invention to provide containerswith aeration and venting for an apparatus and/or method for testing thethermal oxidation tendency of fuels utilizing a test sample to determineif solid particles will form in the fuel at an elevated temperature andpressure.

It is another objective of the present invention to provide a samplecontainer to retain and aerate the fuel being tested and a wastecontainer to receive spent fuel after the test as part of an apparatusand method for determining thermal oxidation stability of fuel bytesting a sample at an elevated temperature and pressure to determine(1) deposits that form on a metal surface and (2) solid particles thatform in the fuel.

It is another objective of the present invention to provide an apparatusand method for holding a test sample, aerating the test sample,delivering the test sample as needed for testing and collecting thespent test sample after the test.

It is yet another objective of the present invention to provide anaeration device to keep a test sample saturated with dry air during athermal oxidation stability test.

It is another objective of the present invention to have an apparatusand method to deliver a test fuel saturated with dry air to a thermaloxidation stability test and collect spent fuel after the test,containers for the test fuel and spent fuel being easily connected andmonitored to make sure the containers are properly connected.

A sample container arm is provided that (1) threadably connects to thesample container and (2) plugs into the apparatus for testing thermaloxidation stability of fuels. The sample container arm performs thefollowing functions:

-   -   (a) connects an aeration frit located in the bottom of the        sample container to an aeration pump;    -   (b) provides a connection to the embedded computer to measure        the temperature of the test sample contained in the sample        container;    -   (c) provides a connection so that the sample drive pump can draw        a test sample from the sample container when performing the        test;    -   (d) provides a vent connection to atmosphere to maintain the        sample container at a atmospheric pressure; and    -   (e) uses the temperature sensor connected to the imbedded        computer to determine if the sample container arm along with the        sample container are in position.        The sample container arm also has a seal to secure it to the top        of the sample container with the sample container arm.

A waste container arm also connects to the apparatus performing thethermal oxidation stability test. The waste container arm resembles thesample container arm. The waste container arm also has a seal to secureit to the top of the waste container with the waste container arm. Thewaste container arm performs the following functions:

-   -   (a) Receives spent or waste fuel after the test has been        performed thereon;    -   (b) Receives vented and/or flushed fuel or air from the test        apparatus during start-up or shut-down;    -   (c) Provides a vent to atmosphere to maintain the waste        container at atmospheric conditions; and    -   (d) Provides an electrical feedback to the embedded computer        indicating the waste container arm and the waste container are        in position.

To ensure the test sample is fully aerated prior to the test, a glassfrit is connected on the lower end of the aeration line inside of thesample container. The aeration frit is made out of coarse glass bondedto a cap that attaches to the aeration fitting. This configurationallows unimpeded airflow into the test liquid.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a general block diagram of a thermal oxidation stability testapparatus illustrating flow and electrical controls.

FIGS. 2 and 2A are a more detailed block diagram showing a thermaloxidation test apparatus used to perform the ASTM D3241 Standard.

FIG. 3 is a pictorial diagram of the coolant flow for FIGS. 2 and 2A.

FIG. 4 is a pictorial diagram of the airflow in FIGS. 2 and 2A

FIG. 5 is a pictorial diagram showing flow of the test sample in FIGS. 2and 2A.

FIG. 6A is a perspective view of the sample container.

FIG. 6B is a perspective view of the internal components of the samplecontainer.

FIG. 7A is a perspective view of the waste container.

FIG. 7B is a perspective view of the internal components of the wastecontainer.

FIG. 8A is an elevated view of the aeration frit.

FIG. 8B is a cross sectional view of FIG. 8A along section lines 8B-8B.

DESCRIPTION OF THE PREFERRED EMBODIMENT

FIG. 1 is a schematic block diagram of a thermal oxidation stabilitytester referred to generally by the reference numeral 20. The thermaloxidation stability tester 20 has an embedded computer 21 with a touchscreen 23 for user interface. While many different types of programscould be run, in the preferred embodiment, applicant is running C++ inthe embedded computer 21. The touch screen 23 displays all of theinformation from the thermal oxidation stability tester 20 that needs tobe conveyed to the user. The user communicates back and forth with theembedded computer 21 through the touch screen 23. If a batch of fuel isto be tested, a test sample is put in the sample delivery system 25.

It is important to the test to make sure the test sample is oxygensaturated through aeration. Therefore, the embedded computer 21 operatesa sample aeration control 31 for a period of time to make sure thesample is fully aerated. The aeration of the sample takes place at thebeginning of the test.

The embedded computer 21 turns on a sample flow control 27, which is apump used to deliver the sample throughout the thermal oxidationstability tester 20. Simultaneous with the sample flow control 27pumping the test sample throughout the system, sample pressure control29 maintains a fixed pressure throughout the system. It is important tomaintain pressure in the system to prevent boiling of the test samplewhen at elevated temperatures. In the present thermal oxidationstability tester 20, the sample is maintained at approximately 500 psiwhen undergoing the thermal oxidation stability test.

Also, the embedded computer 21 controls parameters affecting theintelligent heater tube 33. The test data is recorded to the intelligentheater tube 33 via intelligent heater tube writer 35 from the embeddedcomputer 21. Critical test parameters are recorded on a memory device(as described subsequently) on an end of the intelligent heater tube 33via the intelligent heater tube writer 35. The rating of the depositformed on the intelligent heater tube 33 will be recorded on the memorydevice at a later time.

In performing the thermal oxidation stability test on a test sample, theintelligent heater tube 33 is heated by tube heater control 37. The tubeheater control 37 causes current to flow through the intelligent heatertube 33, which causes the intelligent heater tube 33 to heat up to thetemperature setpoint.

To prevent the hot intelligent heater tube 33 from heating other partsof the thermal oxidation stability tester 20, bus-bar coolant control 39provides coolant to upper and lower bus-bars holding each end of theintelligent heater tube 33. This results in the center section of theintelligent heater tube 33 reaching the prescribed temperature while theends of the intelligent heater tube 33 are maintained at a lowertemperature. This is accomplished by flowing coolant via the bus-barcoolant control 39 across the ends of the intelligent heater tube 33.

The test parameters, such as the dimension of the heater tube, pressureof the test sample or flow rate are fixed by ASTM D3241. However, thecontrol of the equipment meeting these parameters are the focus of thisinvention.

Referring now to FIGS. 2 and 2A in combination, a schematic flow diagramis shown connecting the mechanical and electrical functions. Theembedded computer 21 and the touch screen 23 provide electrical signalsas indicated by the arrows. A test sample is contained in the samplecontainer 41. To make sure the sample in the sample container 41 isfully aerated, an aeration pump 43 is turned ON. The aeration pump 43pumps air through a dryer 45 where the air is dehumidified. From thedryer 45, a percent relative humidify sensor 47 determines the humiditylevel of the pumped air and provides that information to the embeddedcomputer 21. Assuming the percent humidity of the pumped air issufficiently low, the test procedure will continue pumping air throughthe flow meter 49 and aeration check valve 50 into the sample container41. During aeration, flow meter 49 should record approximately 1.5liters of air per minute. Since the flow meter 49 runs for approximatelysix minutes, the aeration pump 43 will sparge approximately nine litersof air into the test sample. This is sufficient time to saturate thetest sample with dry air.

Within the sample container 41, a sample temperature measurement 51 istaken and provided to the embedded computer 21. The sample temperaturemeasurement 51 is to ensure that the test sample is between 15°-32° C.If the test sample is outside of this temperature range, results can beimpacted. Therefore, if the test sample is outside this temperaturerange, the embedded computer 21 would not let the test start.

Once the test sample has been aerated and if all the other parametersare within tolerance, then the sample drive pump 53 will turn ON. Thesample drive pump 53 is a single piston reciprocating pump, also knownas a metering pump. With every stroke of the piston, a fixed volume ofthe sample is delivered. The speed of the sample drive pump 53 iscontrolled so that it pumps 3 mL/min of the test sample. The sampledrive pump 53 is configured for fast refill which minimizes the need formanual pump priming. Pulsations associated with pumps of this design areminimized with the use of a pulse dampener and a coil tubing on theoutlet side as will be subsequently described.

To get air out of the tubing between the sample container 41 and thesample drive pump 53 at the start of the test, an auto pump primingvalve 55 is opened, a sample vent valve 54 is closed and the aerationpump 43 is turned ON by the embedded computer 21. The auto pump primingvalve 55 opens and remains open while a combination of sample and air isdischarged into waste container 57. At the same time the aeration pump43 provides positive pressure in the sample container 41 to force testsample from the sample container 41 to the sample drive pump 53. Thesample vent valve 54 closes to prevent venting of the air pressure toatmosphere and to maintain a pressure of 2 to 3 psi. A sample vent checkvalve 56 across the sample vent valve 54 opens at 5 psi to prevent thepressure in the sample container 41 from exceeding 5 psi. Once thesample drive pump 53 starts pumping the test sample, auto pump primingvalve 55 will close and the sample vent valve 54 will open. Thereafter,the sample drive pump 53 will pump the test sample through check valve59 to the prefilter 61. The check valve 59 prevents fluid from flowingbackwards through the sample drive pump 53. The check valve 59 operatesat a pressure of approximately 5 psi. The check valve 59 preventssiphoning when the sample drive pump 53 is not pumping. Also, checkvalve 59 prevents fluid from being pushed backwards into the sampledrive pump 53.

The prefilter 61 removes solid particles in the test sample that couldaffect the test. The prefilter 61 is a very fine filter, normally in theorder of 0.45 micron in size. The purpose of the prefilter 61 is to makesure particles do not get into the test filter as will be described. Theprefilter 61 is replaced before every test.

From the prefilter 61, the test sample flows through an inlet 63 intothe cylindrical heater tube test section 65. Outlet 67, whileillustrated as two separate outlets, is actually a single outlet at theupper end of the cylindrical heater tube test section 65. Extendingthrough the cylindrical heater tube test section 65 is the intelligentheater tube 69, which is sealed at each end with ceramic bushings ando-rings (not shown). While the test sample flows through the cylindricalheater tube test section 65 via inlet 63 and outlet 67 and around theintelligent heater tube 69, the housing of the cylindrical heater tubetest section 65 is electrically isolated from the intelligent heatertube 69. Only the test sample comes in contact with the center sectionof the intelligent heater tuber 69. Inside of the intelligent heatertube 69 is a thermocouple 71 that sends a signal back to the embeddedcomputer 21 as to the temperature of the center section of theintelligent heater tube 69.

Test sample flowing from the cylindrical heater tube test section 65flows through a differential pressure filter 73, commonly called the“test filter”. The intelligent heater tube 69 heats up the test sampleinside of the cylindrical heater tube test section 65 to the testparameter set point. Heating of the test sample may result indegradation of the test sample, or cause solid particles to form. Thesolid particles may deposit on the center section of the intelligentheater tube 69, and/or may collect in the differential pressure filter73. The pressure drop across the differential pressure filter 73 ismeasured by differential pressure sensor 75. Pressure across thedifferential pressure filter 73 is continuously monitored by theembedded computer 21 through the differential pressure sensor 75. Whenthe pressure across the differential pressure filter 73 exceeds apredefined pressure difference of approximately 250 mm to 280 mm ofmercury, the differential pressure bypass valve 77 opens to relieve thepressure. By test definition, exceeding a differential pressure of 25 mmHg results in failure of the test sample.

For this test to be performed, the test sample must remain as a liquid.At testing temperatures of 250° C. to 350° C., many hydrocarbon fuelswill transition to the vapor phase at ambient pressures. To keep thetest sample in the liquid phase, the back pressure regulator 79maintains approximately 500 psi pressure in the system. This systempressure is monitored by the system pressure sensor 81, which reportsinformation to the embedded computer 21. During a test, normal flow of atest sample is through differential pressure filter 73 and through theback pressure regulator 79. From the back pressure regulator 79, thetest sample flows through sample flow meter 83 to waste container 57.The sample flow meter 83 accurately measures the flow rate of the testsample during the test. The sample flow meter 83 provides sample flowrate information to the embedded computer 21.

A system/safety vent valve 85 is connected into the system andcontrolled via the embedded computer 21. The system/safety vent valve 85acts to relieve excess system pressure in the case of power loss,improperly functioning system components or other system failures. Inthe event of this occurrence, the system pressure sensor 81 sends asignal to the embedded computer 21, triggering the system/safety ventvalve 85 to open and relieve excess pressure. Also, at the completion ofa test, the system/safety vent valve 85 opens to vent pressure from thesystem. The system/safety vent valve 85 is normally set to the openposition requiring a program command from the embedded computer 21 toclose the system/safety vent valve 85. Therefore, if power is lost, thesystem/safety vent valve 85 automatically opens.

At the end of the test, after the system/safety vent valve 85 is openedand system pressure is relieved, the flush air pump 87 turns ON andflushes air through flush check valve 89 to remove the test sample fromthe system. The flush air pump 87 pushes most of the test sample out ofthe system via the system/safety vent valve 85 into the waste container57.

The system may not operate properly if there are air pockets or airbubbles in the system. During a test, it is important to maintain anair-free system. Therefore, at the beginning of each test, the solenoidoperated differential pressure plus vent valve 91 and the differentialpressure minus vent valve 93 are opened, flushed with test sample, andvented to remove any air pockets that may be present. During thebeginning of each test, the position of the differential pressure ventvalves 91 and 93 ensure there is no air in the differential pressurelines.

If the waste container 57 is properly installed in position, a signalwill be fed back to the embedded computer 21 indicating the wastecontainer 57 is correctly connected. This also applies for the samplecontainer 41 which sends a signal to the embedded computer 21 when it isproperly connected. The system will not operate unless both the wastecontainer 57 and the sample container 41 are properly positioned.

The center portion of the intelligent heater tube 69 is heated to thetest parameter set point by flowing current through the intelligentheater tube 69. Instrument power supplied for current generation and allother instrument controls is provided through local available power 95.Depending on local power availability, local available power 95 may varydrastically. In some areas it is 50 cycles/sec. and in other areas it is60 cycles/sec. The voltage range may vary from a high of 240 Volts downto 80 Volts or less. A universal AC/DC converter 97 takes the localavailable power 95 and converts it to 48 Volts DC. With the universalAC/DC converter 97, a good, reliable, constant 48 Volts DC is generated.The 48 Volts DC from the universal AC/DC converter 97 is distributedthroughout the system to components that need power through the DC powerdistribution 99. If some of the components need a voltage level otherthan 48 Volts DC, the DC power distribution 99 will change the 48 VoltsDC to the required voltage level.

To heat the intelligent heater tube 69, the 48 Volts from the universalAC/DC converter 97 is converted to 115 Volts AC through 48 Volt DC/115Volts AC inverter 101. While taking any local available power 95,running it through a universal AC/DC converter 97 and then changing thepower back to 115 Volts AC through a 48 Volts DC/115 Volts AC inverter101, a stable power supply is created. From the 48 Volts DC/115 Volts ACinverter 101, power is supplied to the heater tube module 103. Theheater tube module 103 then supplies current that flows through theintelligent heater tube 69 via upper clamp 105 and lower clamp 107. Theheater tube module 103 is controlled by the embedded computer 21 so thatduring a normal test, the thermocouple 71 inside of the intelligentheater tube 69 will indicate when the intelligent heater tube 69 hasreached the desired temperature.

While the center section of the intelligent heater tube 69 heats todesired test set point, the ends of the intelligent heater tube 69 willbe maintained near room temperature. To maintain the ends of theintelligent heater tube 69 near room temperature, a coolant flowsthrough an upper bus-bar 109 and lower bus-bar 111. The coolant insidethe upper bus-bar 109 and lower bus-bar 111 cools the upper clamp 105and lower clamp 107 which are attached to the ends of the intelligentheater tube 69. The preferred cooling solution is a mixture ofapproximately 50% water and 50% antifreeze (ethylene glycol). As thecoolant flows to the coolant container 115, the flow is measured by flowmeter 113. To circulate the coolant, a cooling pump 117 pumps thecoolant solution into a radiator assembly 119. Inside of the radiatorassembly 119, the coolant is maintained at room temperature. Theradiator fan 121 helps remove heat from the coolant by drawing airthrough the radiator assembly 119. From the radiator assembly 119, thecoolant flows into the lower bus-bar 111 then through upper bus-bar 109prior to returning via the flow meter 113.

The flow meter 113 is adjustable so that it can ensure a flow ofapproximately 10 gal./hr. The check valve 123 helps ensure the coolingsystem will not be over pressurized. Check valve 123 will open at around7 psi, but normally 3-4 psi will be developed when running the coolantthrough the entire system.

To determine if the intelligent heater tube 69 is shorted out to thehousing (not shown in FIGS. 2 and 2A), a heater tube short detector 110monitors for a short condition. If a short is detected, the embeddedcomputer 21 is notified and the test is stopped.

On one end of the intelligent heater tube 69 there is a memory device125 to which information concerning the test can be recorded by IHTwriter 127. While a test is being run on a test sample, the IHT writer127 will record information into the memory device 125. At the end ofthe test, all electronic information will be recorded onto the memorydevice 125 of the intelligent heater tube 69, except for the manual tubedeposit rating. To record this information, the intelligent heater tube69 will have to be moved to another location to record the depositrating as determined (a) visually or (b) through a Video Tube DepositRater. At that time, a second IHT writer will write onto the memorydevice 125. The Video Tube Deposit Rater may be built into the system ormay be a standalone unit.

The intelligent heater tube 69 is approximately 6¾″ long. The ends areapproximately 3/16″ in diameter, but the center portion that is heatedis approximately ⅛″ in diameter. Due to very low electrical resistanceof aluminum, approximately 200 to 250 amps of current flows through theintelligent heater tube 69. Both the voltage across and the currentthrough the intelligent heater tube 69 are monitored by the embeddedcomputer 21. Also, the temperature of the center section of theintelligent heater tube 69 is monitored by the thermocouple 71, which isalso connected to the embedded computer 21. The objective is to have thecenter section of the intelligent heater tube 69 at the requiredtemperature. To generate that type of stable temperature, a stablesource of power is provided through the universal AC/DC converter 97 andthen the 48 VDC/115 VAC inverter 101. By using such a stable source ofpower, the temperature on the center section of the heater tube 69 canbe controlled within a couple of degrees of the required temperature.

Referring now to FIG. 3 of the drawings, a pictorial representation ofthe coolant flow during a test is illustrated. Like numbers will be usedto designate similar components as previously described. A pictorialillustration of the heater tube test section 129 is illustrated on thelower left portion of FIG. 3. Coolant from the radiator assembly 119 isprovided to the lower bus-bar 111 and upper bus-bar 109 via conduit 131.From the upper bus-bar 109, the coolant flows via conduit 133 to flowmeter 113. From flow meter 113, the coolant flows through conduit 135 tothe coolant container 115. The cooling pump 117 receives the coolantthrough conduit 137 from the coolant container 115 and pumps the coolantinto radiator assembly 119. If the pressure from the cooling pump 117 istoo high, check valve 123 will allow some of the coolant to recirculatearound the cooling pump 117. FIG. 3 is intended to be a pictorialrepresentation illustrating how the coolant flows during a test.

Likewise, FIG. 4 is a pictorial representation of the aeration systemfor the test sample. Similar numbers will be used to designate likecomponents as previously described. An aeration pump 43 pumps airthrough conduit 139 to a dryer 45. The dryer 45 removes moisture fromthe air to prevent the moisture from contaminating the test sampleduring aeration. From the dryer 45, the dried air will flow throughconduit 141 to humidity sensor 47. If the percent relative humidity ofthe dried air blowing through conduit 141 exceeds a predetermined amountof 20% relative humidity, the system will shut down. While differenttypes of dryers 45 can be used, it was found that Dry-Rite silica geldesiccant is an effective material for producing the desired relativehumidity.

From the percent humidity sensor 47, the dried air flows through conduit143 to flow meter 49, which measures the air flow through conduit 143and air supply conduit 145. From air supply conduit 145, the dried airflows through aeration check valve 50 and conduit 146 to samplecontainer arm mounting clamp 147 and sample container arm 149 toaeration conduit 151 located inside of sample container 41. In thebottom of sample container 141, a glass frit 153 connects to aerationconduit 151 to cause the dried air to sparge through the test sample insample container 41. When the sample container 41 is in place and thesample container arm 149 is connected to the sample container armmounting clamp 147, contact 155 sends a signal to the embedded computer21 (see FIG. 2) indicating the sample container 41 is properlyinstalled.

Referring now to FIG. 5, a pictorial illustration of the flow of thetest sample in connection with FIGS. 2 and 2A is shown in a schematicflow diagram. The test sample is contained in sample container 41, whichis connected via sample container arm 149 to the sample container armmounting clamp 147. Vapors given off by the test sample are dischargedthrough a vent 157, normally through a vent hood to atmosphere.Simultaneously, the sample drive pump 53 draws some of the test sampleout of the sample container 41. The sample drive pump 53 is a singlepiston reciprocating pump connected to a pulse dampener 159. While thepulse dampener 159 may be configured a number of ways, the pulsedampener 159 in the preferred configuration has a diaphragm with asemi-compressible fluid on one side of the diaphragm. This fluid is morecompressible than the test sample thereby reducing pressure changes onthe test sample flow discharged from the sample drive pump 53. Thesample drive pump 53 is connected to auto pump priming valve 55. Duringstart-up, the closed auto pump priming valve 55 opens until all of theair contained in the pump and the lines are discharged into the wastecontainer 57. In case it is needed, a manual priming valve 161 is alsoprovided. Additionally, the aeration pump 43 (see FIG. 2) is turned ONto provide a slight pressure in the sample container 41 of about 2 to 3psi. The sample vent valve 54 closes to prevent this pressure fromescaping to atmosphere. This pressure will help push the fluid samplefrom the sample container 41 to the inlet of the sample drive pump 53.The 5 psi check valve 56 prevents the pressure in the sample containerexceeding 5 psi. During the test, coil 163 also provides furtherdampening in addition to the pulse dampener 159. Check valve 59 ensuresthere is no back flow of the sample fuel to the sample drive pump 53.However, at the end of a test, flush check valve 89 receives air fromflush air pump 87 to flush the test sample out of the system.

During normal operation of a test, the sample fuel will flow throughcheck valve 59 and through a prefilter 61 removing most solid particles.Following the prefilter 61, the test sample flows into the heater tubetest section 129 and then through the differential pressure filter 73.Each side of the differential pressure filter 73 connects to thedifferential pressure sensor 75. Also connected to the differentialpressure filter 73 is the back pressure regulator 79. The pressure onthe system is continuously monitored through the system pressuretransducer 81. If for any reason pressure on the system needs to bereleased, system/safety vent valve 85 is energized and the pressurizedtest sample is vented through the four-way cross connection 165 to thewaste container 57.

At the beginning of the test, to ensure there is no air contained in thesystem, the differential pressure plus vent valve 91 and thedifferential pressure minus vent valve 93 are opened to vent anypressurized fluid through the four-way cross connection 165 to the wastecontainer 57.

In case the differential pressure filter 73 clogs so that thedifferential pressure exceeds a predetermined value, differentialpressure bypass valve 77 will open to relieve the pressure.

To determine the exact flow rate of the test sample through the system,the sample flow meter 83 measures the flow rate of test sample from theback pressure regulator 79 before being discharged through the wastecontainer arm 167 and the waste container clamp 169 into the wastecontainer 57. The waste container 57 is vented all the time through vent171.

Referring to FIGS. 6A and 6B, a sample container 41 and the samplecontainer arm 149 are illustrated in further detail. A glass frit 153 islocated near the bottom of the sample container 41. A glass frit 153connects through aeration conduit 151, elbow 400 in sample container arm149 to sealing connector 402. Sealing connector 402 will mate with areceiving connector in the sample container arm mounting clamp 147 (seeFIG. 4). As air is blown through the glass frit 153 by the air pump 43,the air will form small bubbles and sparge through the test sample.Small bubbles are preferred as they have more surface area and morereadily dissolve in the test sample. More detail will be given on theglass frit 153 herein below.

Also extending to the bottom of the sample container 41 is a suctionline 404 with a coarse filter 406 on the end thereon. While the coarsefilter 406 can be of any particular type, it could be similar glass frit153. The coarse filter 406 is designed to remove larger solid particlesthat may be in the test sample. The suction line 404 connects throughelbow 409 in sample container arm 149 to the suction connector 408. Thesuction connector 408 connects to a mating connector (not shown) in thesample container arm mounting clamp 147 (see FIG. 4).

Also connecting through sample container arm 149 to the top of samplecontainer 41 is vent line 410. The lower end of vent line 410 terminatesbelow sample container arm 149 but at the top of sample container 41.The opposite end of vent line 410 connects to vent connector 412 whichfurther connects to vent 157 (see FIG. 2 and FIG. 5).

Located near the bottom of sample container 41 is a thermocouple 414 formeasuring the temperature of the test sample. The thermocouple 414 sendsa signal through thermocouple connection 416 to thermocouple plate 418in sample container arm 149. In the sample container arm mounting clamp147, an electrical connection with the thermocouple plate 418 will bemade and the signal from the thermocouple 414 will be sent to theembedded computer 21 shown in FIG. 2. Also, if a signal is beingreceived from the thermocouple 414 through thermocouple plate 418, thatindicates the sample container 41 is in position and the test can begin.

Referring to FIGS. 7A and 7B in combination, the waste container 57 andwaste container arm 167 are shown in more detail. The waste containerarm 167 has a vent line 470 connecting to vent connector 472 the same aswas shown in connection with FIGS. 6A and 6B of the sample container arm149. However, the vent line 470 and vent connector 472 in wastecontainer arm 167 connects to the vent 171 for the waste container 57(see FIG. 5).

During the operation of a test, test sample flow line 420 receives thespent sample from the test through sample connection 422. Sampleconnection 422 connects with a mating connector (not shown) in the wastecontainer clamp 169 to receive the spent sample after test from thesample flow meter 83 (see FIG. 2).

Either when starting up a test or shutting down a test, venting orpurging of the system is necessary through vent/purge line 424 andvent/purge connector 426. The vent/purge connector 426 has a matingconnector (not shown) in waste container clamp 169. The vent/purge line424 and vent/purge connector 426 receive any fluid or air dischargedfrom system vent valve 85, differential pressure plus vent valve 91 anddifferential pressure minus vent valve 93. Also any air or fuel from theauto pump priming valve 55 will be received through the vent/purge line424. The vent line 470, test sample flow line 420 and vent/purge line424 all terminate just below the waste container arm 167 in the top ofwaste container 57.

A shorting plate 428 is contained on the face of the waste container arm167. Two electrical connections extend through the waste container clamp169 (see FIG. 5) so that if the two connections are shorted by theshorting plate 428, the embedded computer 21 will know the wastecontainer 57 is in position.

Sealing the top of the sample container 41 and the waste container 57 isa flexible washer 430. It is important that the material of the flexiblewasher 430 is compatible with fuels or similar petroleum-based products.

On the side of both the sample container arm 149 and the wastercontainer arm 167 are indentations 432 that can be used for gripping thecontainer arms thereto for installing or removing the respective clamps147 or 169.

With the exception of providing a connection for the thermocouple 414there through, the sample container arm 149 and the waste container arm167 are essentially identical. However, the spacing on the connectorsare different so that they cannot be mistakenly interchanged. While thesample container arm 149 and waste container arm 167 can be molded as anintegral piece, in this preferred embodiment a fuel resistant epoxy isused to seal both the sample container arm 149 and the waste containerarm 167 into a solid piece.

The sample container arm 149 threadably connects in the bottom thereofto threads 434 in the top of the sample container 41. Likewise, wastecontainer arm 167 threadably connects to waster container 57 throughthreads 436. When either the sample container 41 or the waste container57 is threadably connected in the proper position, flexible washer 430will seal against leakage. The sample container 41 and the wastecontainer 57 are made from a fuel resistant plastic such as plyolefin orglass.

Referring now to FIGS. 8A and 8B, the glass frit 153 is shown in moredetail. The aeration conduit 151 (see FIGS. 6A and 6B) is received inupper opening 438 of fitting 440. Fitting 440 is a standard fitting for⅛″ diameter tubing. The aeration conduit 151 is ⅛″ in diameter. Betweenthe fitting 440 and the glass frit 153 is a frit cap 442. The frit cap442 is machined to receive the lower thread 444 to threadably connectwith fitting 440. On the upper part is inside passage 446 of frit cap442. The lower outside cylindrical portion 448 of the frit cap 442 ismachined to fit just inside of glass frit 153 and has a shoulder 450 toabut the top of the glass frit 153. The frit cap 442 is made from a fuelresistant material so it will not corrode.

While many different types of glass frit 153 could be used, in thispreferred embodiment, Applicant used a coarse frit made out of glassthat has a 12 mm outside diameter, 6 mm inside diameter and 25 mm inlength. To connect the glass frit 153 to the frit cap 442, afuel-resistant adhesive is used. The flexible washer 430 (see FIG. 6B)may be made of a Viton closed cell rubber gasket.

1. An apparatus for testing thermal oxidation stability of a test samplesuch as a hydrocarbon fuel comprising: a source of electric power; aheater tube connected to said source of electric power for flowingcurrent to heat a center section of said heater tube to a predeterminedtemperature; a coolant flow circuit supplying coolant to each end ofsaid heater tube to keep each end thereof near room temperature; anaeration circuit with an aeration pump for pumping air to aerate saidtest sample in a sample container; a test sample flow circuit forflowing said test sample around said center section to heat said testsample to said predetermined temperature, said test sample flow circuitincluding: a sample drive pump pumping said test sample from said samplecontainer around said center section of said heater tube; a differentialpressure filter in said test sample flow circuit after said heater tubeto filter out any solids that may have formed in said test sample whenheated to said predetermined temperature due to oxidation of said testsample; a differential pressure sensor for measuring differentialpressure across said differential pressure filter; a back pressureregulator for maintaining said test sample being pumped by said sampledrive pump at a test pressure high enough to keep said test sample in aliquid phase when heated to said predetermined temperature; a wastecontainer for collecting said test sample after said test; said samplecontainer and said waste container being sealed to prevent spilling ofsaid test sample, yet selectively providing venting to said samplecontainer during said testing.
 2. The apparatus for testing thermaloxidation stability of said test sample as recited in claim 1 whereinsaid aeration circuit includes an aerator in said sample container tosparge air from an aeration pump through said test sample.
 3. Theapparatus for testing thermal oxidation stability of said test sample asrecited in claim 2 wherein said aerator is a coarse glass frit mountednear the bottom of said sample container on an end of an aerationconduit, said coarse glass frit causing small bubbles of air in saidtest sample.
 4. The apparatus for testing thermal oxidation stability ofsaid test sample as recited in claim 3 wherein said coarse glass frithas a fitting between said coarse glass frit and said aeration conduit,a lower end of said fitting being bonded to an upper end of said coarseglass frit.
 5. The apparatus for testing thermal oxidation stability ofsaid test sample as recited in claim 2 wherein said sample container has(a) an aeration conduit connected to said aeration pump and extendinginto said sample container, (b) a suction line from said samplecontainer to said sample drive pump, and (c) a vent line from saidsample container to atmosphere.
 6. The apparatus for testing thermaloxidation stability of said test sample as recited in claim 5 whereinsaid vent line may be selectively closed by a sample vent valve.
 7. Theapparatus for testing thermal oxidation stability of said test sample asrecited in claim 6 wherein said sample container has a thermocoupletherein for measuring temperature of said test sample to determine ifsaid test sample is of a temperature suitable for said testing.
 8. Theapparatus for testing thermal oxidation stability of said test sample asrecited in claim 1 wherein said sample container connects to a samplecontainer arm and said waste container connects to a waster containerarm.
 9. The apparatus for testing thermal oxidation stability of saidtest sample as recited in claim 8 wherein said sample container arm andsaid waste container arm are made of a solid construction.
 10. Theapparatus for testing thermal oxidation stability of said test sample asrecited in claim 8 wherein said sample container arm and said wastecontainer arm have electrical connections therein to indicate if inposition for said testing.
 11. The apparatus for testing thermaloxidation stability of said test sample as recited in claim 1 whereinsaid waste container (1) receives said test sample after said testing,(2) receives a combination of said test sample and air during start upor a ending said testing and (3) vents to atmosphere to remove pressurethere from.
 12. A method of testing a test sample in liquid form forthermal oxidation stability comprising the following steps: aeratingsaid test sample in a sample container with dry air to saturate saidtest sample with oxygen; heating a center section of a heater tube to apredetermined temperature by flowing current there through; cooling eachend of said heater tube by flowing coolant from a coolant flow circuitto said each end; pumping said test sample at a low flow rate aroundsaid center section of said heater tube so that temperature of said testsample is raised to approximately said predetermined temperature; testfiltering with a differential pressure filter said test sample tocollect solids formed in said test sample when heated to saidpredetermined temperature; maintaining an elevated pressure on said testsample during said pumping step sufficient to keep said test sample fromevaporating; discharging said test sample to a waste container; firstventing said waste container to prevent other than atmospheric pressuretherein; second venting of said sample container to atmosphere, andinterrupting said second venting before said pumping step to cause aslightly higher than ambient pressure in sample container during primingfor said pumping step.
 13. The method of testing the test sample inliquid form for thermal oxidation stability as recited in claim 12wherein said aeration step includes sparging air from a coarse glassfrit in said sample container up through said test sample to saturatesaid test sample with air before said pumping step.
 14. The method oftesting the test sample in liquid form for thermal oxidation stabilityas recited in claim 13 wherein said coarse glass frit is bonded to atransition fitting with a fuel resistant adhesive, which transitionfitting connects to the aeration conduit.
 15. The method of testing thetest sample in liquid form for thermal oxidation stability as recited inclaim 13 includes an additional step of first monitoring temperature ofsaid test sample in said sample container to keep said test sample nearroom temperature and second monitoring of said center section to ensuresaid predetermined temperature is maintained during said pumping step.16. The method of testing the test sample in liquid form for thermaloxidation stability as recited in claim 15 wherein said discharging stepincludes said waste container (a) receiving said test sample after saidtesting, (b) receiving a combination of said test sample and air duringpriming or system venting, and (c) removing pressure there from.
 17. Themethod of testing the test sample in liquid form for thermal oxidationstability as recited in claim 12 wherein said sample container (a)during said aeration step sparges air through said test sample, (b)provides a suction line to said test sample during said pumping step,(c) connects a thermocouple in said test sample to an embedded computer,and (d) using the thermocouple signal by said embedded computer toautomatically check if the sample container is installed in place forsaid testing.
 18. A sample container apparatus for use in a testingapparatus for determining thermal oxidation stability of a test sample,said sample container apparatus comprising: a sample container with anopening at the top thereof; a sample container arm closing said opening,said sample container arm being constructed to mate with a samplecontainer clamp in said testing apparatus; an aerator conduit connectingfrom near the bottom of said sample container, through said samplecontainer arm, to said testing apparatus to receive dry air there fromto sparge said test sample; a suction line connecting from near saidbottom of said sample container, through said sample container arm, tosaid testing apparatus to deliver said test sample thereto; a vent lineconnecting from near a top of said sample container through said samplecontainer arm, to atmosphere via a vent hood; and a thermocouple nearsaid bottom of said sample container to measure temperature of said testsample, a temperature signal from said thermocouple feeding through saidsample container arm to said testing apparatus.
 19. The sample containerapparatus for use in the testing apparatus for determining thermaloxidation stability of the test sample as given in claim 18 wherein saidvent line is selectively closed when starting a test to create aslightly higher than ambient pressure in said sample container to forcesaid test sample through said suction line to said testing apparatus.20. The sample container apparatus for use in the testing apparatus fordetermining thermal oxidation stability of the test sample as given inclaim 19 wherein during said selective closing of said vent line,providing pressure relief if said slightly higher than ambient pressureexceeds a predetermined pressure limit.
 21. The sample containerapparatus for use in the testing apparatus for determining thermaloxidation stability of the test sample as given in claim 18 wherein saidsample container seals to said sample container arm.
 22. The samplecontainer apparatus for use in the testing apparatus for determiningthermal oxidation stability of the test sample as given in claim 21wherein said suction line has a filter on a distal end thereof to removelarge particles from said test sample.
 23. The sample containerapparatus for use in the testing apparatus for determining thermaloxidation stability of the test sample as given in claim 18 wherein afrit is located on a distal end of said aeration conduit to sparge saidtest sample with said dry air.
 24. The sample container apparatus foruse in the testing apparatus for determining thermal oxidation stabilityof the test sample as given in claim 23 wherein said frit is made fromglass.
 25. The sample container apparatus for use in the testingapparatus for determining thermal oxidation stability of the test sampleas given in claim 24 further including a transition fitting between saidglass frit and said aeration conduit.
 26. The sample container apparatusfor use in the testing apparatus for determining thermal oxidationstability of the test sample as given in claim 25 wherein saidtransition fitting is bonded to said glass frit with a fuel resistantsealant.
 27. The sample container apparatus for use in the testingapparatus for determining thermal oxidation stability of the test sampleas given in claim 18 wherein said sample container arm has a feedbackplate for receiving said temperature signal and connecting to saidtesting apparatus when said sample container is in position for testing.